Jim, I put these same sub-frame connectors on my 67. They hit my floor board so I notched the floor board and welded them in solid the the floor boaards. This was a hassle but I think this makes the structure much stronger.

The front of the sub-frame connector slides between the subframe and the bushing/bolt. Bolts/Nuts are included to be used on the side of the subrames where the instructions tell you to drill holes and install the Bolts/Nuts thru where the sub-frame and the connectors overlab. I did not do this. Instead, I welded the connectors to the sub-frame.

The back goes under the leaf spring brackets. My back tabs did not line up. the outer tabs needed to be raised up about 3/16". So I cut them off, bolted them to the body and tacked them. Then, I took them off and welded the in solid. After bolting these in, I welded them as well.